An inhibitor of tubulin polymerization (IC50 = 0.53 μM); arrests the cell cycle at the G2/M transition (IC50 = 92 nM); preferentially cytotoxic to cycling cells; has antiproliferative activity in various cancer cell lines (IC50s = 24-144 nM) and in cell lines resistant to other tubulin inhibitors (IC50s = 20-77 nM); reduces tumor growth in a mouse xenograft model of human amelanoic melanoma at doses of 200 and 400 mg/kg,